A significant amount of Uranium 236 and Neptunium 237 was confirmed on the Moon in 2009,[2] but was known about as early as 1972.[3] Uranium 236 is a radioactive nuclear waste which is found in spent nuclear and reprocessed Uranium. Neptunium 237 is a radioactive metallic element and a by-product of nuclear reactors and the production of Plutonium. These elements have never been found to occur naturally.